The present invention relates to systems for controlling the flow of pressure medium to a hydraulic load. In particular it relates to systems for controlling a hydraulic control member itself constituting the hydraulic load by means of a main valve which determines the direction of flow to the load under control of a pilot valve, flow control means also being provided.
In a known system of the above-described type, a flow sensor is disposed in the outlet line connecting the outlet port of the main valve to the receptacle receiving the pressure medium. In this flow sensor, the magnitude of the pressure difference corresponds to the amount of flow therethrough. This has the distinct disadvantage, when the regulatory region is large, the accuracy for small flows is very small due to the hysteresis of the sensor and because in this case absolute values are being dealt with. A further disadvantage is that the system is not readily adaptable to various commercial applications, for example to applications wherein only a predetermined number of different flows are required. These systems are further subject to malfunction and require a relatively high manufacturing accuracy. Further, the pilot valve operates in an analog fashion and thus makes the arrangement expensive.